1. Field of the Invention
The invention relates to a multiple glazing unit comprising, within the context of the invention, at least three substrates, of the glass substrate type, which are held together by a frame structure, in which at least two intermediate gas-filled cavities each lie between two substrates.
The invention relates more particularly to a triple glazing unit comprising three substrates that are held together by a frame structure, in which two intermediate gas-filled cavities each lie between two substrates.
The invention also relates to the use of substrates for manufacturing thermal-insulation and/or solar-protection multiple glazing units.
These multiple glazing units may equally well be intended for fitting into buildings and into vehicles, especially with a view to reducing air-conditioning load and/or preventing excessive overheating (the glazing is then called “solar control” glazing) and/or reducing the amount of energy dissipated to the outside (the glazing is said to be “low-E” or “low-emissivity” glazing) brought about by the ever increasing use of glazed surfaces in buildings and vehicle passenger compartments.
These glazing units may also be integrated into glazing having particular functionalities, such as for example heating glazing or electrochromic glazing.
2. Description of Related Art
One type of thin-layers stack known for giving substrates such thermal-insulation and/or solar-protection properties consists of a functional metallic layer having reflection properties in the infrared and/or in solar radiation, especially a metallic functional layer based on silver or on a silver-containing metal alloy.
In this type of thin-layers stack, the functional layer thus lies between two dielectric films each comprising in general several layers that are each made of a dielectric material of the nitride type, and especially silicon nitride or aluminum nitride or of the oxide type. From the optical standpoint, the purpose of these films that flank the metallic functional layer is to “antireflect” this metallic functional layer.
However, a blocker film is sometimes inserted between a or each dielectric film and the metallic functional layer, the blocker film placed beneath the functional layer, facing the substrate, protects said functional layer during an optional high-temperature heat treatment of the bending and/or tempering type, and the blocker film placed on the functional layer on the opposite side from the substrate protects this layer from any degradation during the deposition of the upper dielectric film and during an optional high-temperature heat treatment of the bending and/or tempering type.
Currently, there are low-E thin-film thin-layers stacks having a single functional layer (denoted hereafter by the expression “functional-monolayer coating”) based on silver, having, when they are mounted in a conventional double glazing unit, consisting of two 4 mm glass sheets separated by a gas-filled cavity comprising 90% argon and 10% air, with a thickness of 16 mm, one of the sheets of which is coated with the functional-monolayer coating, namely the sheet furthest to the inside of the building when considering the incident direction of the solar light entering the building, on its face turned toward the gas-filled cavity (4-16/(Ar-90%)-4 configuration in which the functional-monolayer coating is the inner face called “face 3”):                a light transmission in the visible TL of around 75 to 80%, or even higher;        a light reflection in the visible RL of around 20 to 10%, or less;        a solar factor (also called a “g-value”) of at least 0.6 and around 0.63 to 0.68, or higher; and        a heat transfer coefficient (also called a “U-value”) equal to or less than 1.5 and around 1.2 to 1.1, or even slightly less.        
In a triple glazing structure the substrate bearing the insulating film may be on face 2 and/or on face 3 and/or on face 5 when considering the incident direction of the solar light passing through the faces in increasing order of their number, starting with the outermost face which is denoted by the number 1.
However, by integrating this (or these) insulating film (or films), although effectively improving the thermal insulation by reducing the heat transfer coefficient, there is also a reduction in the light transmission in the visible and a reduction in the g-value.
Thus, the multiple glazing unit appears to be less transparent in the visible than the double glazing unit such as the one presented above, and the energy saving inside the housing through solar radiation is less.